The proposed research investigates both the integration and hemispheric lateralization of semantic information in fluent bilingual speakers. Semantic integration across languages will be assessed with a word-nonword recognition task, using reaction-time as the dependent variable. A comparison of the extent of response facilitation due to semantic similarities among words within the same language and across languages will be made. Lateralization will be assessed with a reaction-time task which measures the time to decide that a word is a member of a prespecified semantic category. Words will be presented to one hemisphere and reaction time differences due to hemisphere of presentation will serve as the measure of lateralization of semantic processing. The experiments investigate two factors which may account for inconsistencies in previous studies on language integration. The first is that of type of language information being processed. In the proposed experiments, confounding of semantic, syntactic, orthographic and phonemic variables is eliminated, allowing an independent assessment of semantic processing. The second factor is that of the relationships between the two languages spoken. Two subject populations will be used--one in which Ss are fluent speakers of Navajo and English and the other in which Ss are fluent speakers of Spanish and English. These pairs are of interest because Navajo and English differ markedly on a conceptual or semantic level, whereas Spanish and English are semantically quite similar. It is hypothesized that Spanish/English speakers will show a high degree of across-language semantic integration whereas Navajo/English speakers will not. In addition, it is hypothesized that those speakers who show a high degree of semantic integration will tend to show some hemisphere lateralization of semantic information, and that opposite hemisphere lateralization of two languages will occur only in those subjects who do not show evidence of across-language semantic integration.